Save user password as a bcrypt hash

* Replace password field by password_hash
* Add User#password attribute
* Implement password hashing and verification with BCrypt mixin

spec/models/user_spec.rb

@@ -24,6 +24,26 @@ describe User do
     it { should_not be_valid }
   end
 
+  context 'when password_confirmation does not match password' do
+    before do
+      user.password_confirmation = 'WRONG'
+    end
+
+    it { should_not be_valid }
+  end
+
+  describe '#hash_password' do
+    it 'is received when #save is sent' do
+      user.should_receive(:hash_password)
+      user.save
+    end
+
+    it 'stores a bcrypt hash of the password' do
+      user.save
+      BCrypt::Password.new(user.password_hash).should == user.password
+    end
+  end
+
   describe '.authenticate' do
     let (:user) { Factory.create(:user) }